The invention relates to torque wrenches in general and more particularly to a torque wrench that disengages at a predetermined adjustable value by electronically sensing torque and releasing force using electronically actuated linkage while simultaneously creating and audible clicking sound.
Previously, many types of torque wrenches have been used to provide an effective means for tightening threaded fasteners to a predetermined value of tension. In the past mechanical wrenches have utilized spring tension to determine the amount of torque applied to tighten a threaded fastener. These wrenches historically employ a mechanism that uses some type of metallic member that is released when the desired torque is obtained, thus striking the housing or other part of the wrench to produce a distinct mechanical release and to produce a distinct sound, such as an audible xe2x80x9cclickxe2x80x9d. Further, industry has developed specialty wrenches that include electronic means for measuring the amount of torque applied to a structure in response to the manual application of force independent of the position of the user""s hand.
A search of the prior art did not disclose any patents that read directly on the claims of the instant invention, however the following U.S. patents are considered related:
Tatsuno in U.S. Pat. No. 5,741,186 teaches an impulse torque generator for a hydraulic impulse torque wrench. The generator includes a liner driven by a rotor. The liner has an inner cavity having two pairs of sealing surfaces around its inner peripheral surface. A main shaft extends through the liner having projections and driving blades that generate the torque on the shaft by abutting the projections.
Grabivac discloses in U.S. Pat. No. 5,662,012 an adjustable click-type torque wrench. Adjustment is accomplished by a carrier nut engaging the rear end of a lever arm that is contiguous with a spring.
U.S. Pat. No. 5,643,089, issued to Hummel, discloses a non-jarring design that resets the wrench without jarring the output shaft after it delivers the preset maximum torque. The wrench utilizes interchangeable output shafts such that a variety of different drive tips may be employed with the same handle. The cam surfaces of the output shafts have unique surfaces to accommodate varying torque value.
Muralidharan in U.S. Pat. No. 5,156,072 discloses a mechanical torque wrench that employs a plurality of levers. A first lever is journalled to an output shaft for rotation and the remaining levers are pivotally secured to a housing adjacent with their ends along the longitudinal direction of the wrench handle. The torque value is adjusted by changing the force to be overcome by the lever to the pivot.
U.S. Pat. No. 5,142,951 issued to Walton discloses a torque wrench that utilizes a hydraulic piston-cylinder assembly, which rotates a member around an axis located perpendicular to the wrench body. A reaction member is attached to the body and is pivoted relative to the axis between different positions extending angularity out from the body.
Rittmann in U.S. Pat. No. 4,982,612 teaches a torque measuring wrench using a deflection beam, with four strain gauges mounted thereon. One gauge is positioned on a reduced cross-sectional area and the other is closer to the ratchet head. A tubular handle encloses a battery-powered control circuit having indicating means, which provides measurements that are independent of the position along the handle at which the force is applied.
U.S. Pat. No. 4,864,841 issued to Heyraud discloses an electronic wrench that employs two strain gauges that are placed on either side of a crosswise plane. An electronic circuit determines and stores a constant factor for calibration, and the value of torque is measured by the strain gauges and displayed.
For background purposes and as indicative of the art to which the invention is related reference may be made to the remaining cited foreign patents.
Currently there is great demand for wrenches that measure the amount of torque applied to a threaded fastener. The ultimate strength of a fastener cannot be achieved without controlling the amount of torque, since too much can easily break the fastener, thereby leaving a stub inside, which creates difficulty in its removal, particularly if the fastener, such as a capscrew or bolt, is attached to a threaded hole. In the past mechanical tools have been used, and, due to wide spread distribution have become a commonplace and relatively inexpensive. There are numerous drawbacks however, as their accuracy is only passable in some circumstances, as it is affected by ambient conditions, deterioration or relaxation of springs due to time also mechanical wear on moving parts. Scales are permanently marked therefore if some degree of improved accuracy is desired it is necessary to calibrate the tool with a separate gauge or fixture.
The most popular type of torque wrench is called a micrometer or clicking torque wrench and has a hollow arm which includes a spring and pawl mechanism for setting torque. Within the hollow arm, the pawl is forced against one end of a bar that is connected to a drive end. The bar and a drive head are pinned to the hollow arm and rotate as torque is applied. The pawl is released when the force applied by the bar increases beyond a set value established by the operator. When released, the bar hits the inside of the arm, thus producing a sound and a distinct feel by a user. The torque value or release point is changed by rotating the handle, which moves on threads for setting. Additionally, values are permanently stamped or imprinted on a scale that is located on an outer surface of the hollow arm.
The accuracy of the wrench is approximately 4% of the rated setting with the calibration process extremely labor intensive. This type of wrench permits a false sense of accuracy as the actual torque applied by the user may be significantly different than the value imprinted on the handle. This results in inaccurate applications of torque since the release point is significantly affected by the temperature, spring rate, mechanical wear that occurs over time, and the rate at which the user applies the torque. None of these factors are compensated for as the scale is permanently imprinted on the handle.
These wrenches also overtorque when the operator continues to apply pressure after release, due to the momentum created by the releasing mechanism. This overtorque may occur without the user even realizing it.
Another well known wrench type is called a xe2x80x9ccam-overxe2x80x9d wrench wherein a ball bearing or roller is held within a detent. A spring holds the ball within the detent and when the torque on the drive overcomes the spring force on the ball, the ball displaces and the ratchet rotates. This wrench is efficient in that it does not create overtorque however, it has all the same problems as a mechanical wrench which is highly reliant on spring characteristics, wear, calibration difficulties, and it is basically more expensive.
In order to overcome the above difficulties, prior art has developed an electronic or digital torque wrench. This type of wrench uses a plurality of strain gauges which are applied to measure deflection in a solid beam member and provide electrical output signals to determine and display torque value. Such torque values are typically displayed on easily readable digital readout devices. These wrenches are appreciably more accurate (0.5%) and display the torque applied to the fastener. The torque values may be stored in a computer memory and used for traceability. The most significant problem that limits the market of this type of wrench is that it does not physically release or click therefore the user must relay on a visual light or an audible buzzer.
Therefore the primary object of the invention is to provide a torque wrench that uses a combination of electronics for accuracy, and a mechanical release and so called xe2x80x9cclickxe2x80x9d that permits the familiar feel that a user has become accustomed to. This combination which is novel and unique relies on old principles known to those knowledgeable in the industry and current state of the art of miniaturized electronics. Further, the size and shape of the invention is well recognized and acceptable to users.
An important object of the invention is that the wrench not only signals the operator by the feel of the release and audible clicking sound, but also by a buzzers light and visual indication of the actual torque value at the time of release.
Another object of the invention is the durability of the wrench. When compared with other torque wrenches presently available, this wrench has few moving parts that are designed so that wear will not affect the torque accuracy.
Still another object of the invention is the elimination of an overtorque problem of prior art due to momentum after release has occurred. The invention provides a visual display the exact torque at the instant of release. Therefore if the user continues to torque the wrench or if the impact of the pawl within the wrench have any effect on the outcome it is immediately realized and may be easily compensated for.
Yet another object of the invention is the ease of adjustment as the electronics include a switch plate with pressure sensitive pads permitting the user to simply dial in the torque value desired and confirm the setting on the visual display.
A further object of the invention is that the wrench is simple to calibrate and does not require matching or replacing components as does prior art in the all mechanical version.
These and other objects and advantages of the present invention will become apparent from the subsequent detailed description of the preferred and other embodiment also the appended claims, further, taken in conjunction with the accompanying drawing.